1. Field of the Invention
The present invention generally relates to signal enhancement in noisy environments, and more particularly, relates to a compact plug-in noise cancellation device that can filter out background noises and retain useful signals.
2. Description of the Prior Art
Signal enhancement may be desired in many applications. For instance, it may be difficult for a doctor to perform auscultation in noisy environments such as ambulance, construction sites, and factories, as background noise will overwhelm a patient's internal body sounds such as heartbeat. It may be hard for a person to make a phone call in noisy environments such as restaurants, conference halls, and streets with a lot of traffic. Also, when soldiers call for close air support (CAS), they are normally very near the frontline where mortar explosions, machine guns, and other types of background noises are overwhelming. Communication quality is compromised in these noisy environments and thus effective signal enhancement is needed to improve the signal-to-noise ratio (SNR) so as to achieve satisfactory communication quality.
Conventional signal enhancement techniques have reasonably good performance when the background noise is stationary, but if background noise is intermittent or non-stationary, then the noise suppression performance is not good. Moreover, conventional signal enhancement techniques cannot deal with intermittent and large amplitude noise where the SNR may be less than zero, that is, the amplitude of the useful signal is much less than that of the background noise. Therefore, it is desirable to have a compact, lightweight and low lost plug-in noise cancellation device that can effectively suppress various kinds of background noises and retain useful signals such as heartbeat in auscultation and speech in phone communications.